In gas phase polymerization, a gaseous stream containing one or more monomers is passed through a fluidized bed under reactive conditions in the presence of a catalyst. A polymer product is withdrawn from the reactor while fresh monomer is introduced to the reactor to replace the removed polymerized product. Unreacted monomer and catalyst is withdrawn from the fluidized bed and recycled back to the reactor.
Ongoing efforts have been directed to increasing the catalyst activity of the various catalyst compositions used to make polyolefins. For example, production of bimodal polyolefins using a mixed catalyst system that includes at least one metallocene catalyst compound requires a large amount of activator and/or a large amount of the metallocene catalyst compound in order to produce commercial quantities of bimodal polyolefins. Such activators are expensive and the amount of activator required to produce an active catalyst for polymerization has been a substantial impediment to the commercialization of metallocene catalysts for polyolefin production.
There is a need, therefore, for improved methods for increasing the catalyst productivity of various catalyst compositions used for making polyolefins.